Currently production tubing for progressive cavity pumps is comprised of various types of steel, commonly in the form of jointed tubing. This is for several reasons. Mainly it is because progressive cavity pumps are run with an additional rod string that is run inside of the jointed tubing to drive the pump rotation. The rods take up a lot of space, and therefore in order to minimize pressure drops, large internal diameter tubes are typically used, especially when high viscosity fluids are involved.
Another reason is to withstand the torque of the rods. The rods which are run inside the tubing turn the rotor portion of the pump, while the stator portion which is connected to the tubing remains stationary. This creates large amounts of torque, which the production pipe must withstand.
Another reason is for tensile strength as the pipe, rods, pump and fluid can be very heavy, so steel is required for tensile purposes.
Unfortunately steel is more susceptible to corrosion than composites and plastics, and when a small hole caused by corrosion in the production tubular occurs, the entire string would need to be replaced, which is obviously not desirable because of the cost.
Accordingly, there is a need in the oil and gas industry to replace jointed production systems that rely on rods and jointed tubing. To this end it is desirable to deploy a hydraulic submersible progressive cavity pump (HSPCP) which is run down hole by a hydraulically driven motor driver as described in the applicant's co-pending patent application.
When deploying a HSPCP and driver, the need for much of these tensile and torque strengths are vastly reduced by running the system down hole. This allows for the deployment of composite or steel alternative materials. These types of alternative materials would be advantageous for corrosion control, and surface friction reduction.
An encased member may be provided which incorporates both the hydraulic conduits and the production conduit; however, for cost reasons, it may be desirable from time to time to use smaller hydraulic conduits encased together or as individual strings in combination with separate and independent alternative material continuous production tubing. This is because, in many situations, due to the high viscosity of the fluid, the production tube is much larger than the necessary hydraulic conduit tubes and the all inclusive encased member surrounding the production tubing and hydraulic conduits can get large and unnecessarily expensive.